The present invention relates to a rare earth activated alkaline earth metal fluorohalide stimulable phosphor, a method for preparing the stimulable phosphor and a radiation image conversion panel by the use of the stimulable phosphor.
As an effective means for replacing conventional radiography is known a recording and reproducing method of radiation images using stimulable phosphors described in JP-A No. 55-12148 (hereinafter, the term, JP-A refers to an unexamined and published Japanese Patent Application).
In the method, a radiation image conversion panel (hereinafter, also simply denoted as panel) comprising a stimulable phosphor is employed, and the method comprises the steps of causing the stimulable phosphor of the panel to absorb radiation having passed through an object or having radiated from an object, sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as xe2x80x9cstimulating raysxe2x80x9d) to release the radiation energy stored in the phosphor as light emission (stimulated emission), photoelectrically detecting the emitted light to obtain electrical signals, and reproducing the radiation image of the object as a visible image from the electrical signals. The panel having been read out is subjected to image-erasing and prepared for the next photographing cycle. Thus, the radiation image conversion panel can be used repeatedly.
In the radiation image recording and reproducing methods described above, a radiation image is advantageously obtained with a sufficient amount of information by applying radiation to an object at a considerably smaller dose, as compared to conventional radiography employing a combination of a radiographic film and a radiographic intensifying screen. Further, in the conventional radiography, the radiographic film is consumed for every photographing; on the other hand, in this radiation image converting method, in which the radiation image conversion panel is employed repeatedly, is also advantageous in terms of conservation of resources and economic efficiency.
The radiation image conversion panel employed in the radiation image recording and reproducing method basically comprises a support and provided thereon a phosphor layer (stimulable phosphor layer), provided that, in cases where the phosphor layer is self-supporting, the support is not necessarily required. The stimulable phosphor layer comprises a stimulable phosphor dispersed in a binder. There is also known a stimulable phosphor layer, which is formed by vacuum evaporation or a sintering process, free from a binder, and which comprises an aggregated stimulable phosphor. There is further known a radiation image conversion panel in which a polymeric material is contained in the openings among the aggregated stimulable phosphor. On the surface of the stimulable phosphor layer (i.e., the surface which is not in contact with the support) is conventionally provided a protective layer comprising a polymeric film or an evaporated inorganic membrane to protect the phosphor layer from chemical deterioration and physical shock.
The stimulable phosphor, after being exposed to radiation, produces stimulated emission upon exposure to the stimulating ray. In practical use, phosphors are employed, which exhibit an emission within a wavelength region of 300 to 500 nm stimulated by stimulating light of wavelengths of 400 to 900 nm. Examples of such stimulable phosphors include rare earth activated alkaline earth metal fluorohalide phosphors described in JP-A Nos. 55-12145, 55-160078, 56-74175, 56-116777, 57-23673, 57-23675, 58-206678, 59-27289, 59-27980, 59-56479 and 59-56480; bivalent europium activated alkaline earth metal fluorohalide phosphors described in JP-A Nos. 59-75200, 6-84381, 60-106752, 60-166379, 60-221483, 60-228592, 60-228593, 61-23679, 61-120882, 61-120883, 61-120885, 61-235486 and 61-235487; rare earth element activated oxyhalide phosphors described in JP-A 59-12144; cerium activated trivalent metal oxyhalide phosphors described in JP-A No. 55-69281; bismuth activated alkaline metal halide phosphors described in JP-A No. 60-70484; bivalent europium activated alkaline earth metal halophosphate phosphors described in JP-A Nos. 60-141783 and 60-157100; bivalent europium activated alkaline earth metal haloborate phosphors described in JP-A No. 60-157099; bivalent europium activated alkaline earth metal hydrogenated halide phosphors described in JP-A 60-217354; cerium activated rare earth complex halide phosphors described in JP-A Nos. 61-21173 and 61-21182; cerium activated rare earth halophosphate phosphors described in JP-A No. 61-40390; bivalent europium activated cesium rubidium halide phosphors described in JP-A No. 60-78151; bivalent europium activated cerium halide rubidium phosphors described in JP-A No. 60-78151; bivalent europium activated composite halide phosphors described in JP-A No. 60-78153. Specifically, iodide-containing bivalent europium activated alkaline earth metal fluorohalide phosphors, iodide containing rare earth metal activated oxyhalide phosphors and iodide containing bismuth activated alkaline earth metal halide phosphors exhibited stimulated emission of high luminance.
Along with the spread of radiation image conversion panels employing stimulable phosphors is further desired an enhancement of radiation image quality, such as enhancements of sharpness and graininess.
The foregoing preparation methods of stimulable phosphors are called a solid phase process or calcination method, in which pulverization after calcination is indispensable and there were problems such that it was difficult to control the particle form affecting sensitivity and image performance.
Of means for enhancing image quality of radiation images are valid preparation of fine particles of a stimulable phosphor and enhancing particle size uniformity of the fine stimulable phosphor particles, i.e., narrowing the particle size distribution.
Preparation of stimulable phosphors in the liquid phase described in JP-A 9-291278 and 7-233369 is a method of obtaining a stimulable phosphor precursor in the form of fine particles by adjusting the concentration of a phosphor raw material solution, which is valid as a method of preparing stimulable phosphor powder having narrow particle size distribution. From the thus obtained phosphor precursor, a stimulable phosphor was obtained by subjecting the precursor to calcination at high temperature to provide stimulated light-emissive ability but its stimulated emission intensity was not sufficient. The radiation image conversion plate employing such a stimulable phosphor exhibiting a relatively low stimulated emission intensity leads to one having a low sensitivity, so that more dose is required to obtain radiation images having image quality of the same level.
An object of the present invention is to obtain a rare earth activated alkaline earth metal fluorohalide stimulable phosphor exhibiting high luminance, to obtain enhanced stimulated emission intensity in a rare earth activated alkaline earth metal fluorohalide stimulable phosphor comprised of fine particles with high homogeneity of the particle size distribution, and to provide a radiation image conversion panel employing the rare earth activated alkaline earth metal fluorohalide stimulable phosphor and exhibiting high sensitivity and high image quality.
An object of the present invention is to enhance the stimulated light emission intensity, i.e., sensitivity of a stimulable phosphor and to provide a rare earth activated alkaline earth metal fluoroiodide stimulable phosphor exhibiting superior sharpness and graininess, a preparation method thereof and a radiation image conversion panel by the use thereof.
An object of the present invention is to provide a method for preparing a impurity-free stimulable phosphor, in which the preparation process is shortened.
The above object of the invention can be accomplished by the following embodiments:
1. A method for preparing an oxygen-introduced rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by the following formula (1):
xe2x80x83(Ba1xe2x88x92xM2x)FBryI1xe2x88x92y:aM1, bLn, cOxe2x80x83xe2x80x83formula (1)
xe2x80x83wherein M1 is at least an alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; M2 is at least an alkaline earth metal selected from the group consisting of Be, Mg, Ca and Sr; Ln is at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er and Yb; and x, y, a, b and c are numbers meeting the following conditions:
0xe2x89xa6xxe2x89xa60.5, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6axe2x89xa60.05 0xe2x89xa6bxe2x89xa60.2 and 0xe2x89xa6cxe2x89xa60.1
xe2x80x83the method comprising the steps of:
(a) preparing an aqueous mother liquor containing BaX2 of not less than 2.0 mol/l and a halide of Ln, in which X is Br or I, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M2, and when a is not zero, the mother liquor further contains a halide of M1,
(b) adding an aqueous solution containing an inorganic fluoride of not less than 5 mol/l to the mother liquor while maintaining the mother liquor at a temperature of at least 50xc2x0 C. to form a crystalline precipitate of a precursor of the stimulable phosphor,
(c) separating the precipitate of the precursor from the mother liquor, and
(d) calcining the separated precipitate;
2. A method for preparing the rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by the foregoing formula (1), the method comprising the steps of:
(a) preparing an mother liquor containing an ammonium halide of not less than 3 mol/l and a halide of Ln, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M2, and when a is not zero, the mother liquor further contains a halide of M1,
(b) adding an aqueous solution containing an inorganic fluoride of not less than 5 mol/l and an aqueous solution containing BaX2 (in which X is Br or I) to the mother liquor while maintaining the mother liquor at a temperature of at least 50xc2x0 C. to form a crystalline precipitate of a precursor of the stimulable phosphor,
(c) separating the precipitate from the mother liquor, and
(d) calcining the separated precipitate;
3. A method for preparing a rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by the foregoing formula (1), the method comprising the steps of:
(a) preparing an aqueous mother liquor containing BaX2 (in which X is Br or I) of not less than 2.0 mol/l, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M2, and when a is not zero, the mother liquor further contains a halide of M1,
(b) adding an aqueous solution containing an inorganic fluoride of not less than 5 mol/l and an aqueous solution containing a halide of Ln to the mother liquor while maintaining the mother liquor at a temperature of at least 50xc2x0 C. to form a crystalline precipitate of a precursor of the stimulable phosphor,
(c) separating the precipitate from the mother liquor, and
(d) calcining the separated precipitate;
4. A method for preparing a rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by the foregoing formula (1), the method comprising the steps of:
(a) preparing an aqueous mother liquor containing an ammonium halide of not less than 3 mol/l, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M2, and when a is not zero, the mother liquor further contains a halide of M1,
(b) adding an aqueous solution containing an inorganic fluoride of not less than 5 mol/l an aqueous solution containing BaX2 (in which X is Br or I) and an aqueous solution containing a halide of Ln to the mother liquor while maintaining the mother liquor at a temperature of at least 50xc2x0 C. to form a crystalline precipitate of a precursor of the stimulable phosphor,
(c) separating the precipitate from the mother liquor, and
(d) calcining the separated precipitate while avoiding sintering of the precipitate;
5. A method for preparing a rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by the foregoing formula (1), the method comprising the steps of:
(a) preparing an aqueous mother liquor containing an ammonium halide of not less than 3 mol/l, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M2, and when a is not zero, the mother liquor further contains a halide of M1,
(b) adding an aqueous solution containing an inorganic fluoride of not less than 5 mol/l and an aqueous solution containing BaX2 (in which X is Br or I) to the mother liquor while maintaining the mother liquor at a temperature of at least 50xc2x0 C. to form a crystalline precipitate of an alkaline earth-metal fluorohalide,
(c) separating the precipitate from the mother liquor, and
(d) mixing the separated precipitate with a halide of Ln and calcining the mixture;
6. The method described in any one of the foregoing embodiments, wherein the formula (1) is represented by the following formula:
(Ba1xe2x88x92xM2x)FI:aM1,bLn
xe2x80x83wherein M1 is at least an alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; M2 is at least one selected from the group consisting of Ca and Sr; Ln is at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb; and x, y and Z are numbers meeting the following conditions:
0xe2x89xa6x0.5, 0xe2x89xa6axe2x89xa60.05 and 0xe2x89xa6b less than 0.2;
7. The method described in any one of the foregoing embodiments 1 to 5, wherein 0xe2x89xa6yxe2x89xa60.2 and 0xe2x89xa6cxe2x89xa60.1;
8. The method described in any one of the foregoing embodiments 1 to 5, wherein 0xe2x89xa6yxe2x89xa60.3 and 0xe2x89xa6cxe2x89xa60.1;
9. The method described in any one of the foregoing embodiments 1 to 6, wherein y=0, c=0, Ln is at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb, and BaX2 is BaI2;
10. The method for preparing the rare earth activated alkaline earth metal fluoroiodide stimulable phosphor described in 2 above, wherein in the step (b), the fluoride and BaX2 are added while the ratio of fluorine to barium is kept constant;
11. The method described in any one of the foregoing embodiments, wherein the inorganic fluoride is ammonium fluoride or an alkali metal fluoride;
12. The method described in any one of the foregoing embodiments, wherein in the step of (d), the separated precipitate is calcined while avoiding sintering of the precipitate;
13. A radiation image conversion panel comprising a phosphor layer containing a rare earth activated alkaline earth metal fluoroiodide stimulable phosphor prepared by the method described in any one of the foregoing embodiments.
The present invention will be described in detail.
In this invention, the precursor of a stimulable phosphor refers to a substance substantially exhibiting no stimulated light emission or no instantaneous emission. An example thereof is a substance represented by formula (1), which has not been exposed under an atmosphere of a temperature of 600xc2x0 C. or more.
Preparation of Precursor Crystal Precipitate and Stimulable Phosphor
Preparation methods of precipitates of a precursor crystal in the foregoing embodiments will now be described.
Preparation Method of the Foregoing Embodiments 1 and 3
BaX2 (X=Br or I), and, if necessary, a halide of M2 and a halide of M1 are introduced into an aqueous medium and dissolved with sufficiently stirring to form an aqueous solution (hereinafter, also denoted as mother liquor), provided that the ratio of BaX2 to the aqueous medium is so adjusted that the BaX2 concentration is not less than 2.0 mol/l, preferably not less than 2.5 mol/l, more preferably not less than 3.5 mol/l, and still more preferably not less than 4.3 mol/l. In this case, a small amount of an acid, ammonia, an alcohol, a water-soluble polymer or a fine powdery water-insoluble metal oxide may be optionally added thereto. The aqueous solution is maintained at a temperature of 50xc2x0 C. or more, preferably 80xc2x0 C. or more, and 98xc2x0 C. or less as the upper limit. Further, an aqueous solution of an inorganic fluoride (e.g., ammonium fluoride, alkali metal fluoride) of not less than 5 mol/l, preferably not less than 8 mol/l, more preferably not less than 12 mol/l, and 15 mol/l or less as the upper limit is added thereto to form precipitates of a precursor crystal of a rare earth activated alkaline earth metal fluorohalide stimulable phosphor.
One feature of embodiment 1 is that a halide of Ln is contained in mother liquor in advance. The halide of Ln is preferably allowed to exist in the mother liquor prior to addition of an inorganic fluoride. Thus, the addition of the halide of Ln results in phosphor precursor particles which occlude Ln mainly in the center of the particle, leading to enhanced durability of phosphor particles and a radiation image conversion panel by the phosphor particles.
Embodiment 3 includes the step of adding an inorganic fluoride and a halide of Ln to the mother liquor, in which the halide of Ln may be added at any time between addition of the inorganic fluoride and before-separating the precursor, and is preferably added simultaneously with the addition of the inorganic fluoride. The manner of adding the halide of Ln is not specifically limited, but it is preferably added at a temperature of 20 to 98xc2x0 C., and more preferably at a temperature close to that of the mother liquor. According to embodiment 3, Ln is distributed from the center to the outer surface of the particle, leading to enhanced durability of phosphor particles and a radiation image conversion panel by the phosphor particles and enhanced balance of luminance.
Preparation Method of the Foregoing Embodiments 2, 4 and 5
A mother liquor containing an ammonium halide (NH4Cl, NH4Br, and NH4I) of not less than 3 mol/l, and preferably not less than 4 mol/l is prepared, with proviso that when x of formula (1) is not zero, the mother liquor further contains a halide of M2, and when a is not zero, the mother liquor further contains a halide of M1, and after these are dissolved, the ammonium halide is added thereto. Further thereto, an aqueous solution of an inorganic halide (e.g., ammonium fluoride, alkali metal fluoride) of not less than 5 mol/l (preferably not less than 8 mol/l, and more preferably not less than 12 mol/l) and an aqueous BaX2 (X=Br, I) solution are added while maintaining the mother liquor at a temperature of 50xc2x0 C. or higher, preferably 80xc2x0 C. or higher, and 98xc2x0 C. or lower as the upper limit. The crystalline precursor of a rare earth activated alkaline earth metal fluorohalide stimulable phosphor can be thus obtained.
In embodiment 2, a halide of Ln is preferably allowed to exist in the mother liquor prior to addition of an inorganic fluoride. Thus, the addition of the halide of Ln results in phosphor precursor particles which occlude Ln mainly in the center of the particle, leading to enhanced durability of phosphor particles and a radiation image conversion panel by the phosphor particles.
Embodiment 4 includes the step of adding an inorganic fluoride and a halide of Ln to the mother liquor, in which the halide of Ln may be added at any time between addition of the inorganic fluoride and before separating the precursor, and is preferably added simultaneously with the addition of the inorganic fluoride. The manner of adding the halide of Ln is not specifically limited, but it is preferably added at a temperature of 20 to 98xc2x0 C., and more preferably at a temperature close to that of the mother liquor. According to embodiment 4, Ln is distributed from the center to the outer surface of the particle, leading to enhanced durability of phosphor particles and a radiation image conversion panel by the phosphor particles and enhanced balance of luminance.
In embodiment 5, a halide of Ln is added after separation of the precursor precipitate and before calcination, thereby leading to enhanced luminance of the phosphor particles and a radiation image conversion panel by the use of the phosphor.
In each of the embodiments (specifically, embodiments 2, 4 and 5), it is preferred that an aqueous inorganic fluoride solution and an aqueous BaX2 solution are added continuously or intermittently so that the ratio of fluorine of the former and Ba of the latter is kept constant. Addition is conducted using a pipe provided with a pump, and preferably in the vicinity of the region vigorously stirred. There is thus formed a precipitate of the phosphor precursor by allowing the reaction to proceed so that an Ba ion is not in excess during the formation of the precipitate.
In embodiments 2, 4 and 5, the aqueous MX2 solution is added preferably in a concentration of not less than 2.0 mol/l, more preferably not less than 2.5 mol/l, and still more preferably not les than 3.5 mol/l, and preferably not more than 5 mol/l as the upper limit. The solution is also added preferably at a temperature 20 to 98xc2x0 C. and more preferably at a temperature close to that of the mother liquor.
Examples of preferred inorganic fluoride used in the invention include hydrogen fluoride, ammonium fluoride, NH4F.HF, and alkali metal fluoride such as potassium fluoride, lithium fluoride and sodium fluoride. An aqueous inorganic fluoride solution is added through a pipe provided with a pump, and in a concentration of not less than 5 mol/l, preferably not less than 8 mol/l, and more preferably not less than 12 mol/l. Using aqueous inorganic fluoride solution of such a concentration, (1) reduction in particle size is enhanced and (2) impurities included within the particle is reduced to form highly purecrystals. Further, (3) narrowed distribution of Ln within the particle are achieved. Using such phosphor particles, there can be obtained a radiation image conversion panel exhibiting superior fading property, superior balance between sensitivity and sharpness and little unevenness in sensitivity.
It is preferred that an inorganic fluoride is added continuously or intermittently while keeping the ration of fluorine to barium constant. Thus, crystals having a homogeneous element composition in the depth direction can be obtained by keeping constant the ratio of F:Ba to be added. There can be obtained a phosphor exhibiting little variation in performance by calcining the crystals. An aqueous inorganic fluoride solution is added preferably at a temperature 20 to 40xc2x0 C.
In cases where a halide of Ln is added in the form of an aqueous solution, the concentration thereof is preferably 0.1 to 1.0 mol/l. In the case of solid, it is added in accordance with the content of the intended phosphor.
Method of Introducing Oxygen
Representative embodiments of the method of preparing an oxygen-introduced rare earth activated alkaline earth metal fluorohalide stimulable phosphor will be described. Oxygen can be introduced by adding a compound represented by the following formula (2) during the process of preparing the phosphor.
Next, the compound represented by formula (2) will be described:
A1BmOnxe2x80x83xe2x80x83formula (2)
wherein A represents a hydrogen atom or at least an element selected from groups 1 and 2 of the periodic table; B represents at least an element selected from groups 13 through 17 of the periodic table; 1 is a positive natural number more than 0; m is a positive natural number more than 0; and n is a positive natural number more than 0. Of the compounds represented by formula (2), representative one is a compound comprised of an oxygen acid (or oxyacid) anion of an element of groups 1 and 2 of the periodic table, and hydrogen, an alkali metal or an alkaline earth metal.
Thus, A is preferably at least one of H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba. Of these H, Na, K, Ca, Sr and Ba are more preferred and H, Na and K are still more preferred. B is preferably B, Al, C, Si, N, P, S, Se, Br or I, and more preferably C, N and S. Of the compounds represented by formula (2), H2CO3, Na2CO3, K2CO3, CaCO3, BaCO3, HNO3, NaNO3, KNO3, Ca(NO3)2, Ba(NO3)2, H2SO4, Na2SO4, K2SO4, CaSO4, BaSO4, HBr, NaBrO3, KBrO3, HIO3, NaIO3, KIO3, HIO4, and NaIO4 are preferred, and Na2CO3, K2CO3, HNO3, NaNO3, KNO3 AND Ba(NO3)2 are more preferred.
The compound represented by formula (2) is added preferably in an amount of 0.00001 to 0.3. mol, and more preferably 0.00005 to 0.2 mol per mol of an alkaline earth metal contained in an alkaline earth metal fluorohalide stimulable phosphor. The amounts within this range result in luminance-enhancing effects.
The effect of addition of the compound of formula (2) is attributable to the fact that the presence of an oxygen containing anion of the compound of formula (2) simplifies control of introducing oxygen in the calcination process following the synthesis process of the precursor.
In cases where a phosphor precursor is synthesized in the liquid phase, a compound represented by the following formula (3) is preferably contained in an amount of not less than 5 mg per kg of the precursor:
BmOnxe2x88x92zxe2x80x83xe2x80x83formula (3)
wherein B is at least an element selected from groups 13 through 17 of periodic table; m, n and z each are an integer of 1 or more. In the formula (3), B and m are respectively the element and number of formula (2). Representative compounds of formula (3) are oxyacid anions of the compounds of formula (2). Of the anions, CO32xe2x88x92, NO32xe2x88x92, SO4xe2x88x92, BrO3xe2x88x92, BrO4xe2x88x92, IO3xe2x88x92 and IO4xe2x88x92 are preferred. The presence of this anion in the precursor simplifies control of introducing oxygen in the process of calcination. The content of the anion in the precursor is preferably 5 mg to 2 g, and more preferably 50 mg to 1 g per kg of a precursor. The content of the anion can be determined by ion chromatography. The ion chromatography is preferably carried out in accordance with the following conditions:
Measurement apparatus: DX5A0 Gradient Ion Chromatography (available from DIONEX Corp.)
Measurement conditions:
Column:
guard column, Ion Pac AG11 and
separation column, AS11 (available from DIONEX Corp.)
Eluate condition:
A: 100 mM NaOH
B: ultrapure water
gradient of A/B=1/99 (at the star of analysis) and
30/70 (at the finish of analysis)
Suppressor:
ASRS-II (available from DIONEX Corp.)
external mode
SRS current of 300 mA
Regenerate liquid:
Ultrapure water (supplied by 10 psi of high purity nitrogen)
Detection:
conductivity
Separation Process
The resulting crystal of the phosphor precursor are separated from the solution through filtration or centrifugation, washed sufficiently with liquid such as methanol and dried.
Calcination Process
It is preferred that calcination be carried out with avoiding sintering to undergo uniform reduction reaction of the activator. To the dried crystal of the phosphor precursor was added an anti-sintering agent such as alumina fine powder or silica fine powder, which is adhered to the surface of the crystals to prevent siltering. It is possible to save addition of the anti-sintering agent by choosing the calcination condition.
Further, the phosphor precursor crystals are charged into a heat-resistant vessel such as silica port, alumina crucible or silica crucible and then placed in a central portion of an electric furnace to be calcined without causing the crystals to sinter. The crystals are calcined at a temperature of 400 to 1300xc2x0 C. and preferably 500 to 1000xc2x0 C. The calcination time is dependent on the charging amount of a raw material mixture of the phosphor, the calcination temperature and a temperature at the time of being taken out from the furnace, and preferably 0.5 to 12 hrs.
Calcination is carried out in an atmosphere, e.g., in a neutral atmosphere such as nitrogen gas atmosphere, argon gas atmosphere or nitrogen gas atmosphere containing a small amount of hydrogen gas, weakly reducing atmosphere such as carbon dioxide atmosphere containing a small amount of carbon mono-oxide, or an atmosphere in which a small amount of oxygen is introduced.
Sample Preparation
A given amount of a presursor is dissolved in ultrapure water to make a prescribed amount of an aqueous solution. After subjecting to pretreatment in a cartridge, the solution is measured by ion chromatography.
Pre-treatment cartridge:
OnGuard-Ag (available from DIONEX Corp.).
According to this method, for example, peaks of nitrate ion and sulfate ion are observed at a retention time of 12 min. and 18 min., respectively.
The intended rare earth activated alkaline earth metal fluoroiodide stimulable phosphor can be obatained through calcination. Examples of obtained phosphors inclyde
BaFI:0.005Eu; BaFI:0.001Eu, Ba0.97Sr0.03FI:0.0001K, 0.013Eu;
BaFI:0.0002K, 0.005Eu; Ba0.998Ca0.002FI:0.005Eu;
BaFI:0.005Ce; Ba0.99Ca0.01FI:0.0002K. 0.005Eu; and
BaFI:0.0001Ce,0.0001Tb.
The particles relating to this invention preferably have an average particle size of 1 to 10 xcexcm and are monodisperse, more preferably the average particle size of 1 to 5 xcexcm and the distribution of particle size of not more than 20%, and still more preferably the average particle size of 1 to 3 xcexcm and the distribution of particle size of not more than 15%. The average particle size is a mean value of sphere equivalent diameters of 200 particles which are selected at random from the electron micrograph.
Preparation of Panel, Phosphor Layer, Coating, Support and Protective Layer
As supports used in the radiation image converting panel according to the invention are employed a various types of polymeric material, glass and metals. Materials which can be converted to a flexible sheet or web are particularly preferred in handling as a information recording material. From this point, there are preferred plastic resin films such as cellulose acetate films, polyester films, polyamide films, polyimide films, triacetate films or polycarbonate films; metal sheets such as aluminum, iron, copper or chromium; or metal sheets having a said metal oxide covering layer.
A thickness of the support depends on properties of the material, and is generally 80 to 1000 xcexcm and preferably 80 to 500 xcexcm in terms of handling. The surface of the support may be glossy or may be matte for the purpose of enhancing adhesiveness to a stimulable phosphor layer. The support may be provided with a subbing layer under the stimulable phosphor layer for the purpose of enhancing adhesiveness to the phosphor layer
Examples of binders used in the stimulable phosphor layer according to the invention include proteins such as gelatin, polysaccharide such as dextran, natural polymeric materials such as arabic gum and synthetic polymeric materials such as polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, vinylidene chloride/vinyl chloride copolymer, polyalkyl (metha)acrylate, vinyl chloride/vinylacetate copolymer, polyurethane, cellulose acetate bytylate, polyvinyl alcohol and linear polyester. Of these binders are preferred nitrocellulose, linear polyester, polyalkyl (metha)acrylate, a mixture of nitrocellulose and linear polyester, a mixture of nitrocellulose and polyalkyl (metha)acrylate and a mixture of polyurethane and polyvinyl butyral. The binder may be cured with a cross-linking agent.
The stimulable phosphor layer can be coated on a subbing layer, for example, according to the following manner. Thus, an iodide-containing stimulable phosphor, a compound such a phosphite ester for preventing yellow stain and binder are added into an optimal solvent to prepare a coating solution in which phosphor particles and particles of the compound(s) are uniformly dispersed in a binder solution.
The binder is employed in an amount of 0.01 to 1 part by weight per 1 part by weight of the stimulable phosphor. A smaller amount of the binder is preferred in terms of sensitivity and sharpness of the radiation image converting panel and a range of 0.03 to 0.2 parts by weight is preferred in terms of easiness of coating.
A ratio of the binder to the stimulable phosphor (with the proviso that in the case of all of the binder being an epoxy group-containing compound, the ratio is that of the compound to the phosphor) depends on characteristics of the objective radiation image converting panel, the kind of the phosphor and an addition amount of the epoxy group-containing compound.
Examples of solvents used for preparing a coating solution of a stimulable phosphor layer include lower alcohols such as methanol, ethanol, isopropanol and n-butanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; esters of a lower fatty acid and lower alcohol such as methyl acetate, ethyl acetate and butyl acetate; ethers such as dioxane, ethylene glycol ethyl ether and ethylene glycol monomethyl ether; aromatic compounds such as tolyol and xylol; halogenated hydrocarbons such as methylene chloride and ethylene chloride; and a mixture thereof.
There may be incorporated, in the coating solution, a variety of additives, such as a dispersing agent for improving dispersibility of the phosphor in the coating solution and a plasticizer for enhancing bonding strength between the binder and phosphor. Examples of the dispersing agent include phthalic acid, stearic acid, caproic acid and oleophilic surfactants. Examples of the plasticizer include phosphate esters such as triphenyl phosphate, tricresyl phosphate and diphenyl phosphate; phthalate esters such as diethyl phthalate, dimethoxyethyl phthalate; glycolic acid esters such as ethylphthalyethyl glycolate and dimethoxyethyl glycolate; and polyesters of polyethylene glycol and aliphatic dibasic acid such as polyester of triethylene glycol and adipinic acid, and polyester of diethylene glycol and succinic acid.
There may be incorporated, in a coating solution of the stimulable phosphor layer, stearic acid, phthalic acid, caproic acid and oleophilic surfactants for the purpose of improving dispersibility of the stimulable phosphor particles. The plasticizer may optionally incorporated. Examples of the plasticizer include phthalate esters such as diethyl phthalate and dibutyl phthalate; aliphatic dibasic acid esters such as diisodecyl succinate and dioctyl adipinate; and glycolic acid eaters such as ethylphthalylethyl glycolate and butylphthalylbutyl glycolate.
The coating solution as prepared above was uniformly coated on the surface of the subbing layer to form a coating layer. Coating can be carried out by conventional coating means, such as doctor blade, roll coater and knife coater. Subsequently, the coated layer is gradually dried to complete formation of the stimulable phosphor layer on the subbing layer. The coating solution of the stimulable phosphor layer can be prepared by using a dispersing apparatus, such as a ball mill, sand mill, atriter, three-roll mill, high-speed impeller, Kady mill and ultrasonic homogenizer. The prepared coating solution is coated on a support by using a doctor blade, roll coater or knife coater and dried to form the stimulable phosphor layer. After the above coating solution may be coated on a protective layer and dried, the stimulable phosphor layer may be adhered to the support.
Examples of europium activated barium fluoroiodide stimulable phosphor are mainly described herein but preparation of stimulable phosphors including europium activated barium fluoroiodide and others can be performed with reference to the foregoing.
Of phosphors represented by formula (1), the following phosphors are preferably employed to prepare a radiation image conversion panel:
1) a rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by the following formula (A):
(Ba1xe2x88x92xM2x)FI:yM1, zLnxe2x80x83xe2x80x83formula (A)
xe2x80x83wherein M2 is at least an alakaline earth metal selected from Sr and Ca, M1 is at least an alkali metal selected from the group consisting of Li, Na, K, Rb, and Cs; Ln is at least one element selected from Ce, Pr, Sm, Eu, Gd, Tb, Tm and Yb; and 0xe2x89xa6xxe2x89xa60.5, 0xe2x89xa6yxe2x89xa60.05 and 0 less than zxe2x89xa60.2;
2) phosphor of formula (1), in which 0xe2x89xa6yxe2x89xa60.2 and 0 less than cxe2x89xa60.1;
3) phosphor of formula (1), in which 0 less than yxe2x89xa60.3 and 0 less than cxe2x89xa60.1.